ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS Vol. 340, No. 2, April 15, pp. 287–298, 1997 Article No. BB979911 The Effect of Fasting/Refeeding and Insulin Treatment on the Expression of the Regulatory Genes of Ketogenesis in Intestine and Liver of Suckling Rats Gladys Arias, Guillermina Asins, Fausto G. Hegardt, 1 and Dolors Serra Department of Biochemistry, School of Pharmacy, University of Barcelona, 08028 Barcelona, Spain Received October 11, 1996, and in revised form January 14, 1997 in both intestine and liver. The ketogenic rate of both organs was decreased to 40% by long-term insulin The influence of fasting/refeeding and insulin treat- treatment. The different effects of refeeding and insu- ment on ketogenesis in 12-day-old suckling rats was lin treatment on the expression of both genes, on the studied in intestine and liver by determining mRNA ketogenic rate, and on ketone body concentrations are levels and enzyme activity of the two genes responsi- discussed.  1997 Academic Press ble for regulation of ketogenesis: carnitine palmitoyl Key Words: carnitine palmitoyl transferase I; mito- transferase I (CPT I) and mitochondrial HMG-CoA syn- chondrial HMG-CoA synthase; insulin; starvation; thase. Fasting produced hardly any change in mRNA suckling rats; ketogenesis; transcriptional control; in- or activity of CPT I in intestine, but led to a decrease testine; liver. in mitochondrial (mit.) HMG-CoA synthase. In liver, while mRNA levels and activity for CPT I increased, neither parameter was changed in HMG-CoA synthase. The comparison of these values with the ketogenic Ketogenesis in suckling rats takes place mainly in rate of both tissues under the fasting/refeeding treat- small intestine and liver (1, 2). This process is absent ment shows that HMG-CoA synthase could be the main in the fetus and weak in newborn rats, but it increases gene responsible for regulation of ketogenesis in suck- markedly in these organs when the neonate starts ling rats. The small changes produced in serum ketone suckling, so after the first day of life ketone body syn- bodies in fasting/refeeding, with a profile similar to thesis is several times higher than in the fetus (3). This the ketogenic rate of the liver, indicate that liver con- increased ketogenesis is accompanied by an increase tributes most to ketone body synthesis in suckling rats under these experimental conditions. Short-term insu- in the activity of the two main regulatory enzymes of lin treatment produced increases in mRNA levels and this process, i.e., carnitine palmitoyl transferase I (CPT activity in CPT I in intestine, but it also decreased both I) 2 (4) and mitochondrial (mit.) 3-hydroxy-3-methylglu- parameters in mit. HMG-CoA synthase. In liver, graphs taryl-CoA (HMG-CoA) synthase (5). The bell-shaped of mRNA and activity were nearly identical in both curve for ketogenesis throughout the suckling period genes. There was a marked decrease in mRNA levels parallels the enzymatic activities for both CPT I and and activity, resembling those values observed in mit. HMG-CoA synthase (6 – 8). Experiments carried adult rats. As in fasting/refeeding, the ketogenic rate out in our laboratory have shown that in liver and in- correlated better to mit. HMG-CoA synthase than CPT testine there is a close correspondence between keto- I, and liver was the main organ regulating ketogenesis genesis and the mRNA levels for CPT I and mit. HMG- after insulin treatment. Serum ketone body concentra- CoA synthase, suggesting a common mechanism con- tions were decreased by insulin but recovered after trolling the expression of these two genes (9, 10). the second hour. Long-term insulin treatment had lit- Coincident with the increase in ketone bodies in tle effect on the mRNA levels for CPT I or mit. HMG- suckling rats throughout the suckling period, serum CoA synthase, but both the expressed and total activi- concentrations of free fatty acids are high during devel- ties of mit. HMG-CoA synthase were reduced by half 2 Abbreviations used: mit., mitochondrial; HMG-CoA, 3-hy- 1 To whom correspondence should be addressed at Unidad de Bio- quı ´mica, Facultad de Farmacia, Diagonal 643, 08028 Barcelona, droxy-3-methylglutaryl coenzyme A; CPT I, carnitine palmitoyl transferase I. Spain. Fax: /34 3 402 1896. E-mail: hegardt@far.ub.es. 287 0003-9861/97 $25.00 Copyright  1997 by Academic Press All rights of reproduction in any form reserved.